Let's write the EVL() function for X#...

[FoxProMatt]

This discussion is good, letting me see all the things I was NOT thinking about.

I'm anxious to get the basic VFP functions working soon so that when an old VFP dog learns about X# and they do give it a try but the basic functions are not yet implemented, if will be a big let down for them, and they will there badly of VFP.

[atlopes]

Matt,

If X# supports empty dates and datetimes (I'm not working with the machine where I have X# installed right now, so I can't verify this), then YEAR(someDate) or YEAR(someDatetime) should return 0 in case of emptiness.

[Zdeněk Krejčí]

Is it possible to use generics like c#?
Zdeněk

[lumberjack]

Is it possible to use generics like c#?
Zdeněk

Yes!

Code: Select all

LOCAL x AS List<String>
x := List<String>{}
x:Add("abc")
x:Add(123) // Error at compile time

You can also define your own generic classes.

[FoxProMatt]

lumberjack - He's talking about using generics to implement EVL().

Let's not take this thread off on a tangent with code examples of new X# programming examples. X# must implement the EVL() function as-written without users having to change their code, so that's what I want to stay focused on here in this thread.

[mainhatten]

Hi Antonio,

In VFP, in general, any function that accepts a .NULL. for one of its arguments returns .NULL. as a result.
...
Obvious exceptions are NVL(), ISNULL(), and VARTYPE().

"most" would be better. There are string functions not following that rule, but they are few - I had mentioned that missing Nullcheck in xSharp quite a while back. Uncertain if those should be implemented only in vfp dialect calling base implementation, base implementation needs to be enhanced or new implementation (for 1-3 liners, cutting out method call) are appropriate. Will check when new version is available to non-FoXers and if not done perhaps do it in 1 swoop for those I calling my attention early on.

regards
thomas

[mainhatten]

Hi Robert,

The string type in .Net has a Chars property which is an indexable collection of characters in the string. No allocation is needed as far as I know to address individual characters .
The string class is written in CPP:
You can see here that it simply indexes the character in the buffer
https://github.com/dotnet/coreclr/blob/ ... ve.cpp#L52

interesting - might speed up my GetWord* functions if not already tweaked by Chris or you.

regards
thomas

[Zdeněk Krejčí]

Code: Select all

FUNCTION EVL(eExpression1 AS USUAL, eExpression2 AS <T>) AS USUAL
If IsEmpty(eExpression1)
  Return eExpression2
Endif
Return eExpression1
....

[robert]

Zdenek,
What would the benefit of this be over

FUNCTION EVL(eExpression1 AS USUAL, eExpression2 AS USUAL) AS USUAL
If IsEmpty(eExpression1)
Return eExpression2
Endif
Return eExpression1

Robert

[atlopes]

Robert

The string type in .Net has a Chars property which is an indexable collection of characters in the string. No allocation is needed as far as I know to address individual characters .

I've been trying this for a bit in the context of Matt EVL() draft. I'm probably missing something, but since Chars is a String collection, this won't work until a) we create a new string from the Usual parameter, and thus facing a string replication problem again; or b) we have a different implementation of the EVL() function for strings.

Code for option a)

Code: Select all

Case dataType == "C"

  LOCAL emptyChars = " " + CHR(9) + CHR(10) + CHR(13) AS String
  LOCAL testString = uValue.ToString() AS String

  FOR VAR idx = 0 TO testString.Length - 1
    If (emptyChars.IndexOf(testString.Chars[idx]) == -1)
      Return uValue
    Endif
  NEXT

  Return uReturnValue

Code for option b)

Code: Select all

Function Evl (sValue AS String, uReturnValue)

  LOCAL emptyChars = " " + CHR(9) + CHR(10) + CHR(13) AS String

  FOR VAR idx = 0 TO sValue.Length - 1
    If (emptyChars.IndexOf(sValue.Chars[idx]) == -1)
      Return sValue
    Endif
  NEXT

  Return uReturnValue

End Function

Handling of .NULL. seems a problem, really, and appearing in various places, as Thomas mentioned. I found out that I can't even issue

Code: Select all

? .NULL.

without raising an error.